A 1.00 L flask is filled with Ar by water displacement at 20.0°C. the atmospheric pressure is 759.6 torr. after correcting for water vapor pressure in the flask, determine how many moles of Ar are present
Use PV = nRT and solve for n.
Look up the vapor pressure of H2O at 20 C. It is approximately 20 torr BUT that's just a guess (although a very close guess).
Ptotal = pH2O + pAr
You know ptotal and pH2O, solve for pAr and use that for P in PV = nRT. Substitute the other numbers and solve for n. Don't forget T must be in kelvin.
To determine the number of moles of Ar (argon) present in the flask, we need to use the ideal gas law equation:
PV = nRT
where:
P = pressure (in atmospheres)
V = volume (in liters)
n = number of moles
R = ideal gas constant (0.0821 L·atm/mol·K)
T = temperature (in Kelvin)
First, we need to convert the given atmospheric pressure from torr to atm. Since 1 atm = 760 torr, the atmospheric pressure is 759.6 torr / 760 torr/atm = 0.9987 atm.
Next, we need to correct for the water vapor pressure at 20.0°C. The water vapor pressure at this temperature is 17.5 torr. So, we subtract this from the atmospheric pressure to get the pressure of the argon gas only:
Ar pressure = Atmospheric pressure - Water vapor pressure
= 0.9987 atm - 17.5 torr / 760 torr/atm
= 0.9768 atm
Now, we can rearrange the ideal gas law equation to solve for the number of moles (n):
n = PV / RT
Substituting the given values:
P = 0.9768 atm (argon pressure)
V = 1.00 L (volume)
R = 0.0821 L·atm/mol·K (ideal gas constant)
T = temperature in Kelvin
However, the temperature is given in °C, so we need to convert it to Kelvin by adding 273.15:
20.0°C + 273.15 = 293.15 K
Now, we plug in the values and calculate:
n = (0.9768 atm * 1.00 L) / (0.0821 L·atm/mol·K * 293.15 K)
= 0.0418 mol
Therefore, there are approximately 0.0418 moles of argon present in the flask.